The broad objective of this renewal is to advance our understanding of pathophysiological mechanisms of human cardiorenal syndrome (CRS) as defined by the presence of systolic heart failure and renal dysfunction with the goal of developing novel therapeutics and diagnostics for the patients. In the first funding cycle, we investigated the biological interaction between diuretic therapy, the renin-angiotensin- aldosterone-system (RAAS) and cyclic 3?-5?-guanosine monophosphate (cGMP) pathway in human CRS. Specifically, we accomplished the following: 1) Demonstrated that short term (3 weeks) reduction of furosemide dose was well tolerated in patients with chronic systolic heart failure (HF) and improved renal function only in those with renal dysfunction; 2) Utilizing urine proteomics methods, we discovered that Annexin A1 is a potential urine biomarker of CRS; 3) Preliminary data from our grant on the potential renal specific actions low dose nesiritide lead to the design and completion of the ROSE-AHF study carried out within the NHLBI Heart Failure Clinical Research Network. The ROSE-AHF study demonstrated that low dose nesiritide was not renal specific with an increased incidence of hypotension and did not enhance renal function in patients with acute HF and renal dysfunction. Hence, emphasizing the need for a renal specific therapy for human CRS. Specific Aim 1 will determine the efficacy of a novel renal specific peptide, ANX-042, which was designed based on alternatively spliced B-type natriuretic peptide (BNP) discovered by the applicant and colleagues in enhancing GFR without significant hypotension in human CRS. We have identified an alternatively spliced mRNA for B-type natriuretic peptide (ASBNP) that includes a unique and distinct longer carboxyl-terminus. Based on this mRNA, we biodesigned a truncated peptide form (ANX-042) containing the first 13 amino acids of its C-terminal. In experimental heart failure, ANX-042 has potent diuretic and natriuretic actions without the vasodilatory hypotensive properties. In a recently completed First-in-Human study, we have demonstrated that ANX-042 is safe and that it activates its second messenger cGMP at doses that did not result in symptomatic reduction of blood pressure in healthy humans. Our objective is to determine, for the first time, if ANX-042 will enhance renal function without hypotension in patients with systolic HF and renal dysfunction. Specific Aim 2 will test the hypothesis that urine Annexin A1 (AnxA1) is a biomarker of renal injury in acute HF with renal dysfunction with prognostic value. AnxA1 acts as an important endogenous anti- inflammatory molecule and also participates in regulation of cell proliferation and cell death signaling and promotes efficient phagocytosis of apoptotic cells. We found that urine AnxA1 protein levels were increased in systolic HF patients with renal dysfunction versus those with preserved renal function. Others have reported that urine AnxA1 is a biomarker of glomerular injury. Our objective is to extend our previous findings and determine the prognostic value of AnxA1 as a biomarker of renal injury in acute HF with renal dysfunction. Using the urine specimens from the ROSE-AHF study, we will measure urine AnxA1 to determine whether it predicts the development of worsening renal function or type 1 acute CRS and if it correlates with GFR. Specific Aim 3 will determine the renal actions of LCZ 696, a combined angiotensin receptor/ neprilysin inhibitor, and the renal interaction between LCZ 696 and ANX-042 in human CRS. In the PARADIGM study, LCZ 696 reduced death and heart failure hospitalization in patients with heart failure with reduced ejection when compared to Enalapril. Neprilysin degrades the natriuretic peptides, including ANX-042 and is most abundant in the renal proximal tubules. In experimental heart failure, we have previously demonstrated a synergistic renal enhancing action between Neprilysin inhibitor and natriuretic peptides. Our objective is to determine the renal actions of LCZ 696 and if LCZ 696 will enhance the renal action of ANX-042 in patients with systolic HF and renal dysfunction. Our Specific Aims are as follows: Specific Aim 1 Determine the efficacy of a novel renal specific peptide, ANX-042, in enhancing GFR without significant hypotension in human CRS. Specific Aim 2 Define the prognostic value of urine Annexin A1 as a biomarker of renal Injury in acute CRS. Specific Aim 3 Determine the renal actions of LCZ 696, a combined angiotensin receptor/ neprilysin inhibitor, and the renal interaction between LCZ 696 and ANX-042 in human CRS. To address these objectives related to human CRS, we will pursue translational high definition physiological human studies taking advantage of the extensive clinical facilities, patient populations, the NIH funded Center for Clinical and Translational Science (CCaTS) at the Mayo Clinic and also the biomarker specimen bank of the NHLBI HF Clinical Research Network, which makes our proposed research highly feasible, innovative and of significant clinical importance.